Device for controlling the relative rotary position between a crankshaft and a camshaft

ABSTRACT

In a device for controlling the relative rotary positions of a crankshaft and a camshaft of an internal combustion engine, a drive wheel is connected to the camshaft by way of an angular position control mechanism including a planetary gear arrangement with an annular gear connected to, or part of, the drive wheel, a sun gear mounted on the camshaft and at least one planetary gear disposed between, and in engagement with, the annular gear and the sun gear and rotatably supported on a planetary gear carrier, which is rotatable over a certain angular range by a stationary servomotor for controlling the angular positions of the camshaft relative to the crankshaft.

BACKGROUND OF THE INVENTION

[0001] The invention relates to a device for controlling the adjustment of the relative rotary position between a crankshaft and a camshaft of an internal combustion engine.

[0002] In reciprocating four-stroke piston internal combustion engines, the camshaft is driven at half the rotational speed of the crankshaft in order to operate the charge cycle valves (intake and exhaust valves). The control times of the charge cycle valves, in particular of the intake valves, influence the achievable maximum average gas pressure in the cylinders and thus the torque and its location in the usable rotational speed band as well as the power achievable at the rated rotational speed. With control times which are constant in all the operating ranges of the internal combustion engine it is not possible to fulfill the requirements for an optimum torque profile over the engine speed, a high level of power and low exhaust gas emissions, in particular in internal combustion engines with a wide speed band, for example in spark ignition engines. For this reason, the control times are varied as a function of operating parameters, in particular, the engine speed by, for example, changing the rotary position of the camshaft with respect to the crankshaft during engine operation. This is controlled or regulated as a function of operating characteristic variables, characteristic curves and/or characteristic diagrams. As it is irrelevant for the present invention whether control or regulation is carried out, below “regulate” will also be assumed mean “control” without referring to it each time.

[0003] DE 36 07 256 A1 discloses a device for the controlled adjustment of the relative rotary position of a driven machine part with respect to a driving machine part, or in particular the relative rotary position of a camshaft with respect to a crankshaft of an internal combustion engine. Here, the camshaft is driven by the crankshaft by means of a toothed belt and an externally toothed drive wheel. A servomotor is connected in each case directly, in a rotationally fixed fashion, to the camshaft via its drive shaft and on the other hand to the drive wheel via its casing so that a rotationally contollable connection of the camshaft and drive wheel is achieved by means of a holding torque which is provided by the servomotor. By activating the servomotor it is possible to change the relative rotary position of the drive wheel and the camshaft and thus of the crankshaft with respect to the camshaft. The servomotor acts like a clutch and changes only the rotary position without affecting the transmission ratio between the crankshaft to the camshaft. As the casing of the servomotor rotates with the drive wheel, the electrical power and the control signals however have to be transmitted by means of slip contacts. In addition, the mass of the servomotor increases the rotating masses of the camshaft and its drive, and thus the forces of inertia.

[0004] EP 0 254 058 A2 discloses an adjustment device for a camshaft for controlling the gas intake and exhaust valves of internal combustion engines. The camshaft is composed of a hollow external shaft and a hollow internal shaft mounted therein by means of bearings. While the control cams for some of the valves, the inlet valves or the outlet valves, are shrink-fitted onto the hollow external shaft, the cams for the other valves are rotatably mounted on the external shaft and connected for rotation with the hollow internal shaft. The adjustment device can change the relative rotary position of the internal shaft with respect to the external shaft and thus the rotary position of the exhaust valves with respect to the inlet valves over a limited rotary angle range. At the same time, the rotary positions of the external shaft and of the internal shaft change with respect to a drive wheel, which is driven by the crankshaft.

[0005] The device comprises a planetary gear mechanism in which the drive wheel serves as a planet gear carrier on which the planet gears are rotatably supported by means of planet gear bolts. The planet gears intermesh on the one hand with an annular gear, which is connected for rotation with the casing of a servomotor by means of a side plate, and on the other hand to a sun gear, which is mounted for rotation with the internal shaft. The motor shaft of the servomotor is also connected for rotation with the internal shaft, and thus to the sun gear. If the rotary position between the cams of the inlet valves and of the outlet valves is to remain unchanged while the internal combustion engine is operating, the servomotor is electrically controlled in such a way that actuating pulses which are opposed in terms of the direction of rotation are alternately applied to the servomotor. As a result, given a sufficiently high pulse frequency, a virtually rigid connection is formed between the external shaft and the internal shaft so that the planetary gear mechanism rotates locked with the servomotor and the drive wheel. In order to change the angular position, the servomotor must merely be controlled in such a way that its motor shaft is rotated. A fixed transmission ratio of the planetary gear mechanism, which does not influence the transmission ratio of the camshaft drive, determines to what degree the cams are rotated with respect to one another and in relation to the drive wheel. The servomotor may be controlled as a function of characteristic variables, which are dependent on specific operating states of the internal combustion engine. As a result, the angular position of the cams with respect to one another can be set or controlled in accordance with the engine operating conditions. Here too, the servomotor increases the mass of the inertia of the camshaft.

[0006] It is the object of the present invention to provide a device for adjusting the relative rotary position between a crankshaft and a camshaft which reduces the installation space for the drive of the camshaft, and in which the servomotor is fixed in relation to the internal combustion engine.

SUMMARY OF THE INVENTION

[0007] In a device for controlling the relative rotary positions of a crankshaft and a camshaft of an internal combustion engine, a drive wheel is connected to the camshaft by way of an angular position control mechanism including a planetary gear arrangement with an annular gear connected to, or part of, the drive wheel, a sun gear mounted on the camshaft and at least one planetary gear disposed between, and in engagement with, the annular gear and the sun gear and rotatably supported on a planetary gear carrier which is rotatable over a certain angular range by a stationary servomotor for controlling the angular positions of the camshaft relative to the crankshaft.

[0008] The step-down ratio i₂ which is expediently greater than 1 is obtained between the hollow wheel and the sun gear and it provides, as a product together with the step-down ratio i₁ between the crankshaft and the drive wheel, the overall step-down ratio i_(ges). As a result, a step-down ratio i₂ of less than two may be selected and the dimensions of the step-down gearing between the crankshaft and the drive wheel may be made smaller. In addition, the casing of the servomotor is connected fixed in terms of rotation to the casing of the internal combustion engine so that a simple connection with the power supply and with the control unit is obtained and the mass of inertia of the arrangement is increased only insignificantly. The control unit can advantageously be directly mounted on the servomotor or integrated into it, resulting in a compact design and short control drive path.

[0009] The installation space can also be reduced by forming the drive wheel and the annular gear of the planetary gear mechanism in one piece. In the same way, the gear mechanism wheel for controlling the relative rotary position of the camshaft with respect to the crankshaft can be integrally formed with the planet carrier. The relative rotary position between the crankshaft and the camshaft is changed by the electric servomotor in that it rotates the gear mechanism wheel through a desired angular distance by means of its motor shaft and an output element, said distance being predefined by the control device as a function of engine operating parameters. All the transmission means, which are known from gear mechanism technology and are suitable, can be used as drive elements. A simple and expedient solution has proven to be a worm on the motor shaft of the servomotor, which intermeshes with the externally toothed gear mechanism wheel on the planet carrier. However, beveled gears or other gear mechanism elements, which result in actuating torques being transmitted with as little play as possible and a low level of noise, can also be used. It for example is possible to use obliquely toothed gear mechanism wheels, which can also be engaged together free of play with respect to one another.

[0010] The reaction torques of the planet carrier are supported on the casing by means of the servomotor. So that the position of the planet carrier is held even without a servomotor being energized, the servomotor can be equipped with a motor brake. A simple solution is provided if the servomotor adjusts the planet carrier by means of a self-locking gear mechanism, for example in that the gear mechanism wheel is formed as a gear which intermeshes with a worm on the motor shaft of the servomotor. As a result of the self-locking, the frictional forces are sufficient to hold the gear mechanism wheel, and thus the planet carrier, in position.

[0011] The actuating torques of the servomotor can be reduced in that the servomotor drives the gear mechanism wheel by means of a plurality of gear mechanism stages. In addition, it may be advantageous to load the gear mechanism wheel or a component connected thereto in the direction of a supporting torque by means of a pre-stressed spring element. When there is an actuating movement counter to the supporting force, the actuating torque is supported by the drive torque of the camshaft so that the spring element can be pre-stressed without an appreciable degree of expenditure. When adjustment is carried out in the direction of the supporting torque, counter to the drive torques, the servomotor is supported by the pre-stressed spring element so that an approximately similar actuating torque is obtained in both actuating directions.

[0012] Further advantages will become apparent from the following description of the invention on the basis of the drawing. The drawing illustrates an exemplary embodiment of the invention. The description and the claims contain numerous features in combination. The person skilled in the art will expediently also consider the features individually and combine them to form appropriate further combinations.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a schematic view of a device according to the invention,

[0014]FIG. 2 is a schematic partial longitudinal sectional view of an actuating device, and

[0015]FIG. 3 is a schematic view in the direction of an arrow III in FIG. 2.

DESCRIPTION OF A PREFERRED EMBODIMENT

[0016] The device according to the invention is accommodated in a casing 1 for example in a control casing, of the internal combustion engine, which is not illustrated in more detail. The device comprises a drive gear 3, which is driven by a crankshaft by means of a toothed belt or chain (not illustrated). The drive gear 3 is coupled, fixed in terms of rotation, to an annular gear 4. It can also be formed integrally with the annular gear 4. Then the drive gear structure may be formed integrally onto the external circumference of the annular gear 4 (FIG. 2). The annular gear 4 intermeshes with at least one planet gear 6 which meshes with a sun gear 5 of the planetary gear mechanism. The sun gear 5 is mounted on a camshaft 2 which is rotatably supported in the casing 1 and on which the drive gear 3 is rotatably supported by means of a bearing 20. A planet carrier 7 is rotatably supported in the housing by means of a further bearing 19. The planet gear 6 is rotatably supported on the planet carrier 7. As a rule, a plurality of planet gears 6 are provided evenly distributed over the circumference of the sun gear 5.

[0017] An electric servomotor 10 whose motor housing is attached to the casing 1 is coupled to the planet carrier 7 by means of its motor shaft 11 and an actuating gear mechanism. The actuating gear mechanism comprises a pinion 9 on the motor shaft 11 and a gear mechanism wheel 8, which is connected to the planet carrier 7, or, preferably, is formed integrally there-with. The pinion 9 and the gear mechanism wheel 8 may be embodied in numerous variations, for example as straight-toothed or obliquely toothed cylindrical gears, as a worm-gear, as a spindle gear, or as bevel gears or the like. An actuating gear mechanism with a plurality of gear mechanism stages may also be provided between the motor shaft 11 and the planet carrier 7.

[0018] The planet carrier 7 is rotatably supported but held in position in the casing 1 by means of the holding torque of the servomotor 10 so that the planet gears 6 rotate in the direction of the arrow 16 when the drive wheel 3 is rotated in the direction of arrow 15 and the sun gear 5 is driven together with the camshaft 2, in the direction of the arrow 17. When the position of the planet carrier 7 is fixed, the camshaft 2 has a defined relative rotary position with respect to the crankshaft. If this rotary position is to be changed, the servomotor 10, whose motor shaft 11 is rotated through a defined angular range in the direction of the arrows 18 with the integrally formed-on pinion 9 in the form of a worm, is activated. The degree of adjustment is determined by an electronic control unit 12 as a function of the relevant operating parameters of the internal combustion engine. Depending on the rotation of the pinion 9, the gear mechanism wheel 8 is rotated in the direction of the arrow 14 and then held in the new position.

[0019] In order to retaine the position of the planet carrier 7 when the servomotor is not energized, it is expedient to equip the servomotor with a spring-loaded motor brake 10 a, which engages when the power supply is interrupted, irrespective of whether the servomotor 10 has been switched off or the power supply has failed. Instead of the motor brake, an actuating gear mechanism 8, 9 with a self-locking feature can be used with which it is possible to accommodate the torque on the casing 1 by means of frictional forces. In particular worm gear mechanisms or spindle gear mechanisms are suitable for this purpose. Particularly large adjustment angles can be implemented with the device according to the invention.

[0020] A corresponding, opposed, holding torque is generated at the actuating gear mechanism 8, 9 by the drive torque on the drive wheel 3. In the case of an adjustment counter to the holding torque, the actuating torque of the servomotor 10 is accommodated by the drive torque for the camshaft 2, while, for an adjustment in the opposite direction, it must overcome not only the frictional moments and moments of mass inertia but also the torque resulting from the drive torque for driving the camshaft. In order to load the servomotor 10 uniformly, according to one embodiment of the invention, the gear mechanism wheel 8, or a component which is connected thereto, for example the pinion 9 or the motor shaft 11 or the planet carrier 7, may be biased in the direction of the holding torque by means of a pre-stressed spring element 13. The spring element 13 which may be, for example, a helical spring or any other suitable spring element, biases the servomotor 10 drive shaft in the direction of the holding torque, while it is correspondingly pre-stressed when the actuating movement is in the opposite direction.

[0021] The over-all step-down ratio between the crankshaft and the camshaft 2, i_(ges) must be two to one in a four-stroke internal combustion engine. In order to keep the components of the drive for the camshaft 2 small, it is expedient to divide the overall transmission ratio into a first step-down ratio i₁ between the crankshaft and the drive wheel 3 and a second step-down ratio i₂ of the planetary gear mechanism between the annular gear 4 and the sun gear 5, which results in an overall step-down ratio i_(ges), which is equal to the product of the partial step-down. ratios i₁ and i₂. The device according to the invention thus provides numerous possibilities for using the installation space available for the camshaft drive in an optimum way and reducing the weight and the masses of inertia of the internal combustion engine by means of small components. 

What is claimed is:
 1. A device for controlling the relative rotary positions of a crankshaft and a camshaft of an internal combustion engine comprising a drive wheel connected to said camshaft by way of an angular position control mechanism including a planetary gear arrangement having an annular gear rotatable with said drive wheel, a sun gear mounted within said annular gear, and in radially spaced relationship therefrom, on said camshaft for rotation with said camshaft, a planet carrier supported so as to be rotatable about the camshaft axis, at least one planetary gear supported on said planet carrier and being disposed in the space between, and in engagement with, said annular gear and said sun gear, and a servomotor including an actuating gear mechanism engaging said planet carrier for rotating said planet carrier over a predetermined angular range for controlling the angular position of said camshaft relative to said crankshaft.
 2. A device according to claim 1, wherein said planetary gear mechanism has a step-down transmission ratio (i₂) from the ring gear to the sun gear which is greater than
 1. 3. A device according to claim 1, wherein said drive wheel and said annular gear are an integral part.
 4. A device according to claim 1, wherein said actuating gear mechanism includes a plurality of gear stages.
 5. A device according to claim 1, wherein said actuating gear mechanism includes a circumferentially toothed gear wheel, which is in engagement with said planet carrier and is driven by a pinion which is mounted on the shaft of the servomotor.
 6. A device according to claim 1, wherein the actuating gear mechanism includes a worm gear drive consisting of a helical gear connected to the planet carrier and a worm connected to the shaft of the servomotor.
 7. A device according to claim 6, wherein said helical gear is formed directly on said planet carrier.
 8. A device according to claim 1, wherein the servomotor includes a spring-loaded motor brake, which engages, when said service motor is de-energized.
 9. A device according to claim 1, wherein the actuator gear mechanism is a self-locking arrangement.
 10. A device according to claim 1, wherein the gear mechanism driving said planetary carrier is loaded by a pre-stressed spring element in a direction for accommodating a reaction torque effective on said planet carrier.
 11. A device according to claim 1, wherein the servomotor comprises a control unit, which controls the adjustment of the camshaft as a function of characteristic operating values of the internal combustion engine. 